There is a 'silent' datum transformation that may (or may not) take place when data is imported (Feature Class to Feature Class) to a feature dataset and the datum of the source data differs from the destination feature dataset. Users should be able to select the datum transformation used and get a message about what is happening. I understand that this is logged as bug number NIM007879. This is how I'd like to see the problem addressed:
It'd be good if the user were prompted to select a transformation when importing to a feature dataset. At minimum, the user should be notified of the transformation taking place (or not taking place) and be given the option of interactively selecting the datum that should be used.
It'd also be good to have the option to select the datum transformation/s used for a feature dataset, sort of like an environment variable that can be applied to individual feature datasets. Something like 1) select the 'from' and 'to' coordinate systems 2)select a geographic area where the transformation should be used 3) select the appropriate transformation from a list based on the previous two criteria. If the user hasn't set this up for a given pair of 'from' and 'to' coordinate systems, the user would be prompted to select the appropriate transformation as described in the previous paragraph.
Using the Project tool to explicitly define the appropriate datum transformation doesn't work for this - its output won't go to a feature dataset. Instead, the output goes to the root level of the geodatabase with no error or warning message. That leads to serious confusion. See bug NIM078087, which I understand is being addressed in 10.1 sp1.